1. Field of the Invention
The present invention relates to a light adjustment control technology for a single-lens reflex image capturing apparatus.
2. Description of the Related Art
Conventionally, single-lens reflex cameras have been present among both film-based cameras and digital cameras. When shooting with the firing of the flash (flash shooting) is performed by use of a film-based single-lens reflex camera (hereinafter, referred to as “film-based SLR”) or a digital single-lens reflex camera (hereinafter, referred to as “digital SLR”), the light emission amount of the flash is appropriately adjusted by use of a light adjustment sensor.
For example, in a conventional film-based SLR, as shown in FIG. 17, when flash shooting is performed, of the flash light, light reflected at the subject (hereinafter, referred to as “reflected flash light”) is imaged on the film FL through the taking lens PL1. At this time, the amount of, of the reflected flash light, light reflected at the surface of the film FL is detected by a light adjustment sensor AS1 provided in the vicinity of the bottom of the body of the camera 100 and including an integration circuit comprising a capacitor, so that the light emission amount of the flash can be appropriately adjusted.
On the other hand, in a digital SLR, the surface of a microlens disposed in front of the image sensor substantially regularly reflects the reflected flash light like a mirror-finished surface. For this reason, even if a light adjustment sensor is disposed in a position similar to that in the film-based SLR 100, the light amount that can be detected by the light adjustment sensor is small, so that metering accuracy is low.
Therefore, for example, in the flash shooting, a preliminary flash light emission (hereinafter, referred to as “preliminary light emission”) is performed immediately before a shooting operation to obtain an image for recording (hereinafter, referred to as “actual shooting operation”) by the image sensor is performed. Then, the amount of reflected flash light in the preliminary light emission is detected to thereby obtain the distance between the subject and the camera, a guide number (GN) necessary for the light emission of the flash in the actual shooting operation (hereinafter, referred to as “actual light emission”) is calculated, and the light emission amount in the actual shooting operation (hereinafter, referred to as “actual light emission amount”) can be adjusted based on the calculated guide number.
Examples of the method of detecting the amount of reflected flash light include a method in which as shown in FIG. 18, reflected flash light that is incident through the taking lens PL2 and reflected at a reflecting mirror RM2 provided in front of the image sensor IS2 is detected by a light adjustment sensor AS2 including an integration circuit provided in the vicinity of the finder FD2, through a pentaprism PP2 provided in an upper part of the camera 200. Another example is such that as shown in FIG. 19, with a reflecting mirror RM3 being turned up, reflected flash light that is incident through the taking lens PL3 and reflected at the surface of a shutter screen SC3 provided in front of the image sensor IS3 is detected by a light adjustment sensor AS3 including an integration circuit provided in the vicinity of the bottom of the body of the camera 300.
Moreover, a camera has also been proposed that uses one sensor both as the metering sensor for measuring the brightness of the subject and the light adjustment sensor for adjusting the light emission amount of the flash when a shooting without the firing of the flash (hereinafter, referred to as “normal shooting”) is performed.
However, in the light adjustment sensors provided in the above-described conventional cameras, an IC circuit including an integration circuit is used to detect the amount of reflected flash light, and the structure of the IC circuit is complicated by the inclusion of the integration circuit, which increases the cost of manufacturing.
A method is considered in which the amount of reflected flash light is detected by use of a monitor output obtained by the light receiving element of the sensor for automatic focusing (AF) control (AF sensor). However, the dynamic range of the light receiving element of the AF sensor is generally narrow. For example, when the initial setting is made so that light adjustment is correctly made when the distance between the subject and the camera is between 1 to 4 m, in a case where a subject only several tens of centimeters away from the camera is shot, light adjustment cannot be correctly made, so that light adjustment accuracy is degraded.